The invention relates to a color cathode ray tube with a single screen having a plurality of partitioned elemental screen areas, more particularly, to the structure including a signal source for electron beam scanning correction.
Color cathode ray tubes for large-sized, high brightness, high resolution color TV receivers for use in high defininion TV systems, or for large-sized, high resolution graphic display units for use in computer terminals, demand specification requirements differing from those for color cathode ray tubes applicable to general consumer applications. Various investigations have been carried out to try and meet these specification requirements.
Conventional high brightness, high resolution shadow mask color cathode ray tubes, in small-sized tube configurations, are at present commercially available. However, large-sized tubes with sufficiently high degrees of brightness and resolution have yet to be commercially realized. The main reasons for this shortcoming can be attributed to the increase in the magnification factor of the electron-optics of the electron gun which would necessarily accompany any extended tube depth due to possible increases in tube dimensions. There is a reduction in the electron beam energy intensity on the screen surface as a result of any screen enlargement.
A color cathode ray tube which combines several small-sized, high brightness, high resolution color cathode ray tubes to form a single screen has been proposed in Japanese Patent Publication No. 54-12035. The most significant fact resulting from this method was the junction of the reproduced multi-partitioned screen image. The minimum requirement for the joining of the multi-partitioned screen image is the accurate synchronisation of the transmission time of the video signal, corresponding to the respective partition zones at each of the partitioned screen areas, i.e. the time required for a single scanning line ot trace each of the partition zones, and the time at which deflection scanning is initiated of the effective partition screen.
In general, it is possible to accurately synchronise both of these aforementioned time requirements by carrying out adjustments to the tube drive circuitry. However, over extended times periods deviations arise due to inherent ageing of the color cathode ray tube drive circuitry itself. Also deviations such as thermal deformation to the external and internal member of the tube occur even over short time periods immediately after switch-on and for considerable time periods thereafter.
Consequently, in color cathode ray tubes in which time-related deviations are present, with respect to the video signal and deflection scanning, overlapping of the reproduced image occurs between the small partitioned screen areas, together with the appearance of gaps, which give rise to considerable deterioration in the over all quality of the reproduced picture image.